The invention relates to a group control for elevators in general and, in particular, to a load dependent control of elevator cars.
A typical elevator group control has call registering devices arranged on the floors, by means of which calls for desired floors of destination can be entered, with floor and car call memories assigned to the elevators of the group, which memories are connected with the call registering devices. Upon the input of calls at a floor, a call characterizing the input floor is stored in the floor call memory and the calls characterizing the floors of destination are stored in the car call memory. The control also includes load measuring devices provided in the cars of the group of elevators, which devices are connected with load memories, first and second selectors assigned to each elevator of the group, exhibiting for each floor at least one position, and a device by means of which the entered calls are assigned to the cars of the group of elevators.
Such a group control is shown in the U.S. Pat. No. 4,718,520 wherein the assignments of the cars to the entered calls can be optimized in time. The car call memory of an elevator of this group control consists of a first memory, already containing assigned car calls, and further memories assigned to the floors in which the calls for desired floors of destination entered at the respective floors, not yet assigned to a car, are stored. A control device, by means of which the entered calls are assigned to the cars of the group of elevators, includes a computer in the form of a microprocessor and a comparison device. Immediately after the registering of a call, the computer calculates, during a scanning cycle of a scanning device at every floor, from at least the distance between the floor and the car position indicated by a selector, the intermediate stops to be expected within this distance and the instantaneous car load, a sum proportional to the loss of time of the waiting passengers at the floors and in the car.
If the first scanners encounter a not yet assigned floor call, the calls entered at this floor for desired floors of destination, stored in the further memories of the car call memory, also have to be taken into account. Therefore, an additional sum proportional to the loss of time of the passengers in the car is established and a total sum is formed. This total sum, also called the cost of operation, is stored in a cost memory. During a scanning cycle of a second scanner following immediately thereafter, the costs of operation of all elevators are compared by means of the comparison device, where in each case an assignment command is stored in an assignment memory of the elevator with the lowest cost of operation, which command designates that floor to which the respective car is assigned optimally in time.
In this group control, an entered call can be assigned to a car almost immediately after the registering of the call. In order to timely signal the assigned car to the passengers waiting on a floor, this type of control can be modified in such a manner that a call assigned for the first time to a car remains assigned to that car, until it is taken over and acted upon by the drive control. Thus, the assignment of a call to be serviced in the future is dependent on the car load existing at the time of servicing, which in this group control can be established based on the registered calls for the desired floors of destination. However, there also exists the possibility that passengers board who have not entered any calls, so that on a subsequent stop due to a fixed assigned call by another passenger, the car could become overloaded.
It is therefore the purpose of the present invention to improve the above described group control in such a manner, that a call assigned to a car will always be serviced by the same car, without the possibility of generating an overload at a stop at the respective floor.